Radio measurement of distances and velocities



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RADIO MEASUREMENT OF DISTANCES AND VELOCITIES Filed Jan. 17, 1938 7 Sheets-Sheet 6 Fig. 9

Feb. 4, 1947. -w. w. HANSEN ETAL RADIO MEASUREMENT OF DISTANCES AND VELOCITIES Filed Jan. 17, 1938 7 Sheets-Sheet 7 bivai Patent ed Feb. 4, 1947 RADIO DIEASUREMENT F DISTANCES AND VELOCITES Application January 17, 1938, Serial No. 185,382

20 Claims.

Our present invention is concerned with the location of aircraft and other objects and the measurement of distances and velocities by radio means.

The principal object of the present invention is to provide a novel method and apparatus for locating aircraft or other craft from a remote point, such as from a point on the ground, regardless of visibility or atmospheric conditions.

Another object of the present invention lies in the provision of method and means employing high frequency radio waves for accurately and rapidly determining the distance of an object from a remote point and also, as in the case of an aircraft located from the ground, means is provided for quickly determining the azimuthal and elevational position of the craft as for purposes of anti-aircraft fire control.

Still another object of the present invention is to provide means for enabling the operator of an airplane to determine his position with respect to the ground.

A further object of the invention is to provide means for determining the presence of one craft from a remotely located craft and the measurement of the distance between the craft, as for preventing collision therebetween.

A further object of the invention is to provide means for determining the component of the remote objects velocity along the line extending from the present equipment to the object, or in the event the equipment is installed on a movable object, such as an aircraft, the relative velocity of the objects is determined along such line.

The present invention also provides means for effecting the transmission, modulation, and reception of alternating currents of frequencies of the order of 10 cycles per second corresponding to wave lengths of from a fraction of a centimeter to a few centimeters. Still another object of the present invention is the provision of apparatus that is suitable for locating and/or measuring the distance of objects on the ground or water from an aircraft, or the location of objects at sea from shore or from other fixed points.

The invention has for another object to provide novel apparatus for carrying out the method and measurements above mentioned.

This invention possesses numerous other objects and features of advantage, some of which, together with the foregoing, will be set forth in the following description of specific novel apparatus for carrying out and utilizing the novel method. It is therefore to be understood that 65 Fig. 1 is a schematic View of one form of the the method is applicable to other apparatus, and that we do not limit ourselves to the apparatus of the present application, as we may adopt various other apparatus embodiments, utilizing the method, within the scope of the appended claims.

Part of the means used to accomplish the above objects mentioned are described in Hansen Patent No. 2,190,712 dated February 20, 1940, and in Varian Patent No. 2,242,275 dated May 20, 1941.

In systems for location of aircraft heretofore employed there are generally three elements involved: first, a source of oscillating energy, secand, means for causing that energy to be directed from or reflected from the aircraft (or if the observer is in an aircraft, possibily reflection from the ground) and third, a receiver for the energy. In clear daylight the sun furnishes light which is reflected from the aircraft and which is received by the observer's eye. At night a search light or a transmitter of other waves may direct a beam toward the aircraft and the reflected energy may be received by an observer. Under some conditions the sound of the airplane will disclose to an observer on the ground its location. Our invention is. related to these other systems in a general way, i. e., to the extent that we employ radiated energy, but the means and method of accomplishment are novel. Prior methods and means, generally employing light or sound, have been unsatisfactory in use because of natural limitations involved. Thus, in the case of light, the operated devices are only operative under conditions of good visibility, and in the case of sound operated devices, the obtainable accuracy of location is very poor, so that these methods of locating objects are of limited utility, while our invention is fully operative regardless of weather conditions and has an accuracy comparable with optics. In our invention the use of very high radio frequencies together with novel methods of projection and reception permit accuracy in location of objects under all weather conditions. In addition, the methods and means for projecting and receiving accurately beams of radio radiation provided by the present invention have application to objects other than first mentioned, as, for example, confidential communication between ships at sea. What constitutes a preferred embodiment of the present invention is set forth in the specification following.

For the specification of our invention the figures are as follows:

present invention and illustrates a general mode of operation.

Fig. 2a is a section on a, plane lying in the axes of the reflector element of Fig. 1.

Fig. 2b is a section similar to Fig. 2a, but at right angles thereto.

Fig. 8 is a sectional view of somewhat modified instrumentalities applicable to Figure 1.

Fig. 4 is a schematic wiring diagram applicable to the system of Fig. 3.

Fig. 5 is a representation of a novel type of electromagnetic radiator for broad or fan beam radiation.

Fig. 6 is a representation of a novel type of electromagnetic radiator for narrow or columnar beam radiation.

Fig. '7 is a sectional diagrammatic representation of a novel form of modulated radio fre quency oscillator-amplifier.

Fig. 8 is a sectional representation of a novel radio receiver. 7

Fig. 9 is a receiver circuit diagram applicable to our invention.

Fig. 10 is a schematic assembly view of the apparatus of this invention.

The general mode of operation of our invention in an illustrative application is indicated in Figure 1. In Figure 1 a projector I directs a flat fan-like beam of radiation upward at a variable angle depending upon the angle of elevation of the projector. The beam is of small thickness and of relatively great extent or spread laterally. In thickness the beam is contained within an angle of a few degrees. Laterally its angular spread can be made any convenient angle up to 180. The projector is trunnioned as at 6 so that the angular elevation of the beam is adjustable from 0 to 90 and pivoted on a vertical axis at I so that it can be rotated in azimuth through 360. In this specification the beam of projector I will be referred to as the searching beam.

A second projector 2 producing a columnar beam, is trunnioned and pivoted in connection with projector I so that its beam always has the same angular elevation about axis Ii as the beam of projector I and is rotatable in azimuth therewith, and so that its beam may be rotated laterally within the angular spread of the broad searching beam and in the plane thereof. The beam of projector 2 'will be referred to as the columnar, pencil or spotting beam. In the use of projectors I and 2 the assemblage is pointed in the general direction of the aircraft to be located. The projectors are then rotated in elevation so the searching beam intercepts an aircraft. Then projector 2 is rotated laterally until the spotting beam intercepts the aircraft already located in elevation by the searching beam. Once located, the beams can be moved angularly so as to continue to follow the aircraft'as long as it is in range.

The radiation from projectors I and 2 is reflected by the aircraft and is received by receiver detectors that are similar to the projectors in their geometrical relationships. One receiver detector 3 having a fan-shaped zone of reception is arranged to receive radiation from any point of reflection in the fan searching beam and it is set to the same elevation and azimuth as projector I. A second receiver detector 4 is illustrated in the drawing and is arranged to receive radiation within a small angle only, i. e., this receiver detector has a columnar zone of reception and is set to the same angles as projector 2.

Projector I may be built conveniently using an elongated parabolic reflector 5 indicated in section in Figs. 2a and 2b. The section of Fig. 2b is that of a parabola for focusing radiation from a small source 5' into a parallel-sided beam as in ordinary searchlight practice. The section of Fig. 2a is that required for projecting a diverging beam of a desired angular spread.

The arrangement of the spotting beam projector and receiver in which the projector and receiver elements are separate units, as shown in Fig. 1, can be conveniently replaced by a combination of the two elements in a single assemblage as shown in Figure 3. In this arrangement the projector is made smaller than the receiver and is supported concentrically with it. The assemblage is pivoted and trunnioned as indicated in Figure 1. In Figure 3, II is the receiver reflector, I2 the projector reflector supported by strut members I3, while It is a transmitter at the focus of reflector I 2, and I5 is an absorbing shield concentric with I2 for minimizing scattered radiation that might interfere with the receiver. Inside reflector II near the focus but above and below the same, as shown in the drawings, are placed two receivers I6 and I! which are used to align the assemblage in elevation on the observed aircraft or object. Also, in reflector II on opposite sides of the focus and displaced from I6 and II are shown two other similar receivers I8 and I9 for aligning the assemblage in azimuth on the observed object. In the event that spotting entirely with a columnar beam is desired, then both pairs of receivers IBI'I and I8--I9 are used and but a single transmitter shownat I4 is employed, as shown in Fig. 3. However, in the event that a fan beam is employed for elevation scanning, as in Fig. 1, then the apparatus of Fig. 3 must be duplicated as in Fig. 1, but only two receivers are used with each receiver reflector, one transmitter reflector and receiver reflector in that case serving to provide a fan shaped beam of transmission and zone of reception, respectively. These pairs of receivers as well as the transmitters used in our invention are novel in principles of operation and construction. Also the circuits in which they operate are novel. The instrumentalities themselves and the connections between them are not excessively complicated considering the objects they accomplish, but they are of sufficient complexity to permit considerable variation in details of construction. Accordingly, the description to follow is restricted because of practical requirements of brevity to as simple a delineation as is consistent with clearness. The trunnioning and pivoting of the projectors and receivers, for example, follows conventional searchlight practice so will not be detailed here. The system of operation will be described first and after that the instrumentalities required for its accomplishment.

Fig. 4 shows in schematic form a wiring diagram of the form of our invention shown in Fig. 3, and in which parts corresponding to those in Fig. 3 are similarly numbered. In Figure 4, II is a receiving reflector, I2 is a projecting reflector, I4 is a transmitter radiating by means of an antenna 2| at the focus of reflector I2, I6 and II are receivers with antennas 22 and 23 near the focus of reflector II and above and below it. Since receivers I8 and I9 operate similarly to receivers I6 and II, the former are not shown in the figure in order to simplify the same and the description. Further, the receivers I8 and I9 would not be used in the event the fan shaped scanning beam of Fig. 1 is employed. 24 is a power source for receivers l8 and H; 25 is a master oscillator shown as receiving energy from a source 25 and which delivers high frequency currents to the transmitter M and receivers l6 and I1 and to receivers 18 and [9 in the event that these receivers are used, as when searching with a. columnar beam only; 21 is a high frequency interrupter oscillator subject to frequency modulation by another oscillator 28; 29 is an adjustable frequency interrupter oscillator; 31 is a potentiometer and 32 designates indicating apparatus.

In the ordinary mode of operation of our iiivention the master oscillator 25 oscillates steadily at a high frequency. For convenience this will be assumed to be 3X10 cycles per second corresponding to a wave length of one centimeterl Oscillator 25 delivers to transmitter l4 and to receivers l6 and I1 energy of the high frequency. In transmitter M, the high frequency energy received is amplified and energy at the high frequency is radiated by the antenna 2|. The transmitter I6 is controlled by two interrupter frequency oscillators 21 and 29. One of these, 21

delivers to transmitter Hi a frequency whose half period is of the order of a thousand times the period of the transmitters frequency. This interrupter frequency operating through suitable means at the transmitter causes the latter to radiate in alternate periods corresponding to alternate half cycles of the interrupting frequency, but for a little less than the duration of the half period. Preferably, the interrupter frequency half period should not be much less than a thousand periods of the radiated frequency so as to enable the transmitter to build up its oscillations to a steady value within the periods of operation between interruptions. If the radiated frequency is 3x10 cycles per second, the interrupter frequency can be of the order of 10" cycles per second. The purpose of interrupting the radiated wave is to prevent the transmitter from interfering with the receiver. When the transshow how this is accomplished. Typical apparatus for accomplishing this is disclosed in Proceedings of The Institute of Radio Engineers, vol. 22, No. '1, July, 1934, Transmission lines as frequency modulators, and Bulletin of University of Washington Engineering Experiment Station, Bulletin No. 68, January 2, 1933, Side bands in frequency modulation, by ED. Scott and J. R.

. Woodyard. The frequency at which the change the period of the frequency modulation of the interrupting frequency.' If a factor of 100 is assumed, the period will be 2 l0- seconds or the a frequency will be about 200 cycles per second mitter is off, the receiver is on and vice versa.

The interruption of reception is accomplished by means similar to that controlling transmission, using the interrupter frequency of oscillator 21.

Oscillator 21 is illustrated as controlled by a modulation frequency oscillator 28 which changes the frequency of oscillator 21 about 1% at a frequency of the order of 100 cycles per second, i. e., a range of from about forty to several hundred cycles. The purpose of this is to shift the frequency and wave length of the interrupter frequency periodically so there will be no distances or zones along the radiation beam for which the returned signal is zero long enough for an object at that distance in it to go undetected. The transmitter when operating will send out trains of waves of say 1000 cycles. Then there will be an interval of the same or slightly greater length with no radiation unless the length of the intervals-is changed. The distance corresponding to i 1000 cycles of a 1 centimeter wave is 10 meters. If the distance between the observer and the observed object is 1000 meters, or 100 intervals, a change of 1% in the length of the interval will shift the 100th interval a distance equal to its own length. Inasmuch as the minimum range of an oscillator so it is not deemed necessary to or less. To summarize up to this point, oscillator 25 will deliver a steady frequency of 3x10 oscillator 21! will deliver a frequency of about 10" cycles per second, frequency-modulated about 1% at about 200 cycles per second by oscillator 28. Transmitter I l will thus radiate a frequency of 3x10 cycles per second at slowly varying intervals corresponding to a frequency of about 10" cycles per second. The receivers l'fi and I1 will be operative in the intervals between the sending intervals. If the frequency of oscillator 21 is made sufficiently high or the objects searched for are sufiiciently large, the frequency modulation oscillator 28 may be omitted.

A second interrupter frequency oscillator 29 interrupts the sending and receiving at a fre quencylower than that of oscillator 21. This oscillator is used for determining the distance between the observer and an observed object. Its frequency is variable between limits dependent upon the maximum and minimum ranges in which observations are possible. In the above example, oscillator 21 interrupts the transmitter M at in tervals corresponding to a frequency of 10''. 0scillator 29 interrupts the transmitter for a longer period, 1. e., after it has transmitted a hundred or a thousand or more of the short intervals. The long intervals of interruptions controlled by oscillator 29 are used in determining distance while the short ones controlled by oscillator 21 serve to eliminate interference by the transmitter with the reception of the reflected transmitted waves. In measuring distance from the observer to an observed point, the frequency of oscillator 29 is first adjusted to a higher value than is needed for the actual measurement. It is then gradually decreased by turning knob 29'. At certain frequencies the distance traversed by the radiation is an odd number of half wave lengths of oscillator 29. At these frequencies a pulse of radiation will leave the projector, travel to the observed point and return to the receiver, arriving when the transmitter is off. As the frequency is changed the received signal will vary between zero and a definite maximum. The frequency whose 'wave length is 4 times the distance to the observed point is the lowest frequency that will give an observed maximum in the received signal. Reducing the frequency still further will cause a gradual decrease in the received signal without producing additionalmaxima or minima. Ac-

, cordingly the distance can be determined by reducing the frequency of oscillator 29 until the last maximum is observed and then, for sharpness of the frequency at-which the zero reading preceding the last maximum occurs enables us to read distance directly, 1. e., the indication of the pointer of knob 29' on scale 30. For a distance of 1000 meters it is 75,000 cycles.

' In measuring distance by the methodjust described, oscillator 29 has been referred to as an interrupting oscillator. Actually it is not necessary .or even always desirable for oscillator 29 to interrupt the transmission of waves. Instead, under some circumstances, it is more desirable for oscillator 29 to merely amplitude modulate the transmitted waves sinusoidally.

It will be apparent that the plurality of interrupting frequencies described with reference to Figure 4 need not all be used in all circumstances. For example, when the system is used in aircraft for altimeter purposes wherein a simple measurement to the ground is desired, the interrupter frequency oscillator 21 and its accompanying frequency modulator 28 can be dispensed with. Under these conditions entire control of the transmitter I4 is accomplished by the distance measuring interrupting frequency oscillator 29.

Claims directed to the novel method of measuring distance and to the apparatus therefor are contained in our-divisional application Serial No. 459,039 filed September 19, 1942.

In Figure 3 a cylindrical as of slightly conducting material is shown concentric with reflector I2. This shield is advantageous if the interrupter 21 is not used, and the oscillator and amplifier are in continuous operation while the searching process is in progress. It will be easily seen in Figure 3 that if shield l absorbs most of the limated by the reflector, there will be little radiation diifracted back to the'receivers, and that which so diffracted will be very nearly cancelled because it enters two opposing members of a receiving pair in substantially equal amounts.

In the receiving arrangements, it has been indicated in Figure 3 that there is a pair of receivers it above and I! below the focus of the reflector for determining the angular elevation of the beam and a pair of the focus-for lateral setting. The vertical and lateral circuits are identical electrically although only one member of a pair need be used for distance determinations. In each pair of receivers the output connections are opposed, and the points of reception are located slightly off the reflector axis and on opposite sides of it so that the receivers look at overlapping but slightly offset bits of sky centered slightly on opposite sides of the reflector axis. With such an arrangement,

an object on the reflector axis will excite equal signals in each receiver which will exactly cancel each other, giving zero resultant signal, but if the object is slightly off the axis it will excite one receiver more than the other, giving a resultant signal the slgn of which indicates on which side of the reflector axis the object lies.

Under some-circumstances, the receiver 4 of Fig. 1 may be dispensed with, and all reception performed in receiver 3, in which case the transmitter 2 is swept along the fan beam until a maximum response is obtained from receiver 3.

absorbing shield l5 radiation except that col- Also, projector 2 and receiver 4 may be made similar to I and 8 for broad or fan-shaped beams, but oriented at right angles to I and 3 so the two broad beams intersect to provide sharply defined location of objects at that point and locations in zones by either of the broad beams used instead of-parabolic reflectors.

alone.

The instrumentalities used in the several parts of the system shown in Figures 1 to 4 will now be described. It is principally in the frequencies higher than 10 cycles per second and particularly higher than 10 that our novel means are most valuable. For these frequencies our transmitters and receivers can be adapted conveniently to parabolic reflectors, and in addition they are adaptable to a new type of. projector that can be They can also of course be used for reception.

These novel projectors, in transmission more properly termed radiators, are modifications of the resonant chambers described by W. W. Hansen in his Patent No. 2,190,712. This radiator is essentially a hollow conducting body in which electromagnetic oscillations of definite mode can be established, and from which they can be radiated through suitably placed openings. These resonant chambers or internally resonant hollow conductors are used in several ways in our present invention, and for convenience will be referred to in this specification hereafter as hollow resonators.

Figure 5 shows one illustrative form of hollow resonator suitable for radiating a beam of the I8 and I9 on opposite sides form that would be projected by the arrangement shown in Figures 2a and 2b and indicated at ,l in Figure 1. In Figure 5 the radiator is 11- lustrated; as a hollow resonator 4| of cylindrical form with a slot 42 cut in the side parallel to the axis of the cylinder. The hollow resonator is either excited by one or more inductive loops 43 connected to oscillator or by one or more small jdi-pole antennae 44, or by any other convenient means. The essential feature of this type of radiator is a hollow resonator with a major axis long compared to the wave length of the standstant. The slot does not need to be parallel to the major axis. If these conditions are fulfilled, radiation will emerge from-all the apertures or from the whole slot in phase. The well known laws of difiraction then limit the radiation to a beam collimated in the plane of the major axis. The radiation from the slot is collimated in the axial direction and is diffracted radially as light is diffracted in leaving an optical slit. The behavior analogy to the optical case of the electromagnetic waves in free space after they leave the slit is determinable by use of the diflraction theory of light. The cylinder 4| is mounted on trunnions 45 in the way corresponding to the way the projector l in Figure 1 is mounted. The searching beam is elevated to the desired angle by inclining the axis of the cylinder M from the vertical. The lateral spread of the beam is centered about the radius drawn from the center of the cylinder 4| through the center of the slot these wave lengths the is from about one third of a centimeter to about five centimeters, or may be much more if the resonator is operated on a harmonic of its fundamental frequency.

Figure 6 shows one illustrative form of narrow beam radiator. It comprises a hollow resonator 46 shown as a generally rectangular or approximately square form having a side dimension large in comparison with wave length, and a depth of dimensions approximately lambda/ 2 or in the event that the resonator operates on a harmonic, the depth will be approximately, a multiple of lambda divided by 2 where lambda is wave length. The resonator is either excited by one or more loops 41 or by one or more small di-pole antennae 48 inside driven by oscillators of proper frequency. In one face of the resonator there are holes having diameters which are a fraction of the wave length and conveniently although not necessarily spaced in a circle. The electromagnetie field inside the resonator radiates from each of the holes in phase, the electric vector of the contained field being parallel to the face havin the'holes therein and being of the same phase throughout the immediate region adjoining the face of the resonator. The mutual interference of the radiation from the holes restricts the resultant total radiation to a beam whose axis is perpendicular to the radiating face of the resonator and contained in a cone having an angular spread which is a function of the ratio of the wave length to the dimensions of the pattern of the radiating holes.

With reference to the transmitters for activating antennae such as indicated at 5 in Figures 2a and 2b, and 2| in Figure 4, Figure 7 shows an illustrative form suitable for use inside refiectors or with hollow resonator radiators. assemblage shown uses an oscillator of the kind disclosed in the aforesaid Varian patent, with novel additions necessary in our present invention. In Figure 7, 5| is an evacuated container, 52 is a heated electron emitter, 53 is a hollow resonator with two grids confining a field, 54 is a hollow resonator with one grid and a plate, 55 an electrical coupling between the two resonators, and 55 a collimating grid for maintaining an electric field of the desired form, all of which are shown in the co-pending application referred to. A plate 51 coacts with grid 56 for the delineation of the field used to accelerate the electrons from the emitter 52; a grid 58 is used for controlling the electrons leaving the emitter 52, a tube 59 is used for controlling the electrons in their travel between resonators 53 and 54 and a radiating coupling loop BI is shown in the resonator 54. The grid 58 is connected to a resistor 52, a battery 53 and an oscillator 64. The tube 59 is similarly connected to a resistor 65, a battery 66, and an oscillator 61. The loop 6| is connected to a radiating antenna 68. Another loop 89 connected to an oscillator Ill provides excitation when the assemblage is used as a power amplifier.

In the operation of this combination, oscillations of'a wave length in the region of 1 centimeter to 20 centimeters are produced in the way explained in the co-pending application mentioned above. These oscillations are modulated or periodically interrupted by applying to grid 58 a negative potential with respect to the cathode 52 and impressing thereon an alternating or undulating voltage generated by the oscillator 64, which oscillator corresponds to either or both oscillators 21 and 29 of Fig. 4. The modulation can be accomplished also by applying an un The dulating voltage to the electrode 59 with respect to the potential of the resonators by use of oscillator 61, which also corresponds to oscillators 21 and 29 of Fig. 4. These methods of modulation can be used either together or singly. The frequency of the interrupting potential is subject to the restriction that it should be low enough to permit the oscillation of the resonators to follow the interrupting frequency. We have found that if the interrupting frequency is about one thousandth that of the resonator frequency, as explained in connection with Fig. 4,'the system will operate. The arrangement shown in Figure 7 can be used in several ways. It will act as a self-oscillator by having the two hollow resonators 53 and 54 tuned to the same frequency and exchanging energy between them through the coupling loop 55. It will act as a power amplifier by exciting it at the frequency of the resonators by use of the loop 69 which receives energy from the oscillator 10 corresponding to oscillator 25 of Fig. 4. In such case feed back 55 is adjusted so as to prevent self oscillation. It will act as a frequency multiplier by using the the upper resonator 53 as a buncher at one frequency and tuning the lower resonator to a harmonic of the buncher frequency. As explained in the aforesaid Varian patent, 2,242,275, the electrons leaving resonator 53 will have variable velocities, depending upon the phase of the oscillating circuit while the electrons are passing through, so that accelerated electrons will catch up with retarded electrons, thereby changing the stream of electrons from a uniform beam to one consisting of a series of concentrations or groups or bunches of electrons which pass a given point with the same frequency as the exciting frequency of member 53, so that this member serves as a buncher of the electron stream. In any of its modes of oscillation or amplification, modulation can be accomplished by the introduction of suitable modulation potentials to the grid 58 or the tube'59, or both.

The receivers used in our invention and indicated in Figs. 1, 3, 4 and 10 by the numbers It to Hi inclusive are made in the novel form shown in Figure 8, in which II is an electron emitter, 12 is a collimating grid, 13 is an electron grouping resonator having grids l4 and 15, I6 is a tube fastened between resonator I3 and an energy absorbing resonator 19, I1 and 18 are grids of resonator 19, is a detector electrode, BI is a concentric line for the incoming signal which is delivered to a coupling loop 94, 82 is a concentric line for an incoming heterodyne frequency which is delivered to a coupling loop 95, 83 is a mechanical connection for tuning adjustment of the resonator 13 as to resonant frequency, '85 is an evacuated container with flexible couplings 86 and 81 at the ends, 89 is a mechanical arrangement for adjusting parts 13 and I9 simultaneously as to frequency through links 83 and 84 by relative displacement, i. e., by bodily compressing or expanding the members 13 and 19 as is explained in the aforesaid Varian patent. 16 is a tube giving mechanical support between the two resonators I3 and 19 to which is attached a lever 9| slotted and pinned with a pin 92 to tube 16 91 is a grid for controlling the electron stream,- this grid being connected to oscillators 21 and '11 20. If desired, these oscillators may be connected to separate grids 01 and 08.

The operation of the receiver shown in Figure 8 is somewhat similar to that of a vacuum tube circuit with two tuned circuits. The two resonators are tuned to about the same frequency, An input signal to which resonator I3 is tuned is introduced through the line 8| to the coupling loop 04. This causes the resonator 13 to contain a weak electromagnetic field which acts upon a stream of electrons from the emitter "II as they proceed through the resonator from grid 14 to 15 after being accelerated by a field between the emitter II and collimating grid I2. In addition to the incoming signal at 04, the resonator I3 receives a signal through loop 05 of nearly the same frequency for heterodyning with the input signal. This heterodyning signal combines with the input signal to establish the oscillating electromagnetic field in member I3 that acts on the electron stream to cause the same to become bunched, as described in the aforesaid Varian patent, 2,242,275, as it travels toward the grids I1 and I of the oscillating resonator 19. The resonator I9 oscillates with varying intensity analogously to the plate circuit of an ordinary heterodyne detector as the phase between the signals of loop 94 and loop shifts,

and accordingly it causes the velocity of the electrons emerging from the field between grids I1 and III to vary recurrently at the beat frequency. The electrode 80 is adjusted to a negative potential so that some of the electrons in the stream are deflected away from it while others hit it depending upon their velocities. Two adjustments are possible, one so that almost none of the electrons of normal velocity, 1. e., those passing through where neither the input nor heterodyne signals are supplied, strike the electrode and the other so that nearly all the electrons of normal velocity strike it. In either adjustment,

when a signal is added there will be electrons approaching the electrode with velocities both greater and less than the velocities without the signal. In the first adjustment those electrons of velocities greater than before will hit the electrode so that the current from electrode 80 will increase, In the second adjustment all the electrons of lowered velocity will miss the electrode while those of increased velocity will continue to hit: so the current from electrode 80 will decrease. In either case, the average current from electrode 80 will be a function of the strength of oscillation in I9, as is required for signal detection. The coupling loop 06 between resonators I3 and 19 can be adjusted for such amounts of regeneration between the two circuits as may be desired. The output from electrode 80 being of frequencies in. the ordinary ranges, can be amplified in ordinary vacuum tube circuits. The two grids 91 and 9B are used for modulating or interrupting the output of the detector.

The way in which the detector in Figure 8 is used in the system shown schematically in Figure 4 is indicated by the diagram Figure 9. In Figure 9 the pair of receiver elements for use in either azimuthal or elevational indications, as the case may be, are indicated by the same numbers as in Figure 8. The other parts of the circuit are emitter heating transformers IM and I02 each connected to one of duplicate detectors. These transformers have a secondary winding mid-tap connected adjustably to the negative side of a source I03 of direct current whose positive side is connected through the grounded "0| from the receiving antennas indicated by 22 and 23 in Figure 4 the resonators I3.

is brought by a concentric line I 04 from the master oscillator shown at 25 in Figure 4. This frequency differs by a small percentage from thereceived signal reflected from the observed object depending upon the relative velocities of the observer and the observed object. The difference between these two frequencies determines the frequency of the detected output frequency of the unit. The grids 91 of the two detectors are connected as indicated in Figure 4 to the two oscillators 21 and 29. These oscillators operate at ordinary radio frequencies and can be of conventional vacuum tube design. They impress on to the coupling loops 04 in grids 9I undulating voltages that are capable ofv interrupting the electron streams in the detectors causing them to be on and oif during the alternate half cycles of the controlling currents.

The two electrodes deliver detected currents having frequencies that are the difference between the signal and heterodyning frequencies in resonators 13. The two output currents of the two detectors are brought together at ground through the potentiometer 3|. Connected to the potentiometer there are a number of circuit elements shown in Figure 9 which are indicated by element 32 in Figure 4. Two amplifying tubes I05 and I06 with input and biasconnection of conventional type deliver their plate outputs to a center-tapped transformer I01, the secondary of which drives an amplifier I08. The amplifier I08 acting through a mixed amplifier I09 provides an indication in a zero center meter IIO. Transformer I 01 supplies the difference of the voltage outputs of tubes I05 and I06 to the control grid of tube I00, whereas the sum of the voltage outputs of tubes I05 and I06 is supplied by lead I09 to the auxiliary grid of tube I09 so that the product output of this tube will be the difference of the squares of the voltage outputs of tubes I05 and I06 .suitable for operating the zero center meter IIO. When the two output currents from.

The heterodyning frequency. v

the other side a load 2 equivalent to that of" amplifier III. Amplifier III delivers to indicator II3 of the voltmeter type signals proportional to the output of an individual detector. It also delivers signals to a frequency meter Ill, The indicator H3 is used in determining the distance from the observer to the observed object, and the frequency meter N4 the velocity of the target toward or away from the observer. The operation of the distance meter is as explained in connection with Figure 4 with reference to variation of the frequency of oscillator 29. The measurement of-velocity with the frequency meter 4 depends upon the change in frequency of a wave received from a moving source. If a beam from the projector I2 in Figures 3 and 4 is reflected from a target back to apoint near the projector, such as receiver II, the frequency, because of the Doppler effect, will be increased when the distance is decreasing and will be decreased when the distance is increasing. The difference between the frequency of the transmitted and received signals will be proportional to the velocity toward or away from the observer. This difference of frequencies, as mentioned in connection with Figure 8, will appear in the detected current output of the detectors. Measurement of the frequency by ways already known will indicate the velocity.

The general scheme of operation of the pre-' ferred form of our invention as illustrated can now be summarized, High frequency radio signals are transmitted in pulses by a transmitter M in connection with a reflector l2 or by an oscillator with a radiator of the type shOWn in Figure 6. The transmitted signals are reflected by an observed object which may be an airplane or, if the observer is in an airplane, the ground or another airplane. The received signal is received by any suitable receiver controlled by an oscillator 21 so that the receiver is 01f when the transmitter is sending and vice versa. The intervals of transmission are caused to vary periodically in' length by a low frequency oscillator 28 so that no part of the space near the observed object is unexplored by the signal. The intervals of transmission are sent in groups interrupted in comparatively longer periods by an oscillator 29 which is variable so that the lengths'of the transmitted groups, i. e., the period permitted to transmit each group can be varied. The way the signals are transmitted may be thought of as follows with reference to Figure 4. The oscillator is controlled so that it sends a carrier wave of about 10 cycles per second out up in dots by 21 and sent at the rate of about 10" per second. The strings of dots are cut up by 29 so that they are sent in variable strings of from about 100 to a few thousand. The observer first locates a target using the arrangement shown in Figure 1. Then with the spotting beam on the target he keeps the spotting beam in alignment on the target by the use of an indicator H0 which indicates zero when alignment is correct. The observer adjusts the frequency of the oscillator 29 until the last periodic reading as the" frequency is de creased indicates range to the target. He determines its velocity by use of the frequency meter H4. In reference to Figures 3 and 9, it will be understood that a pair of receivers connected as shown in Figure 9 would be used, one for lateral finding and one for vertical finding in the system. Only one member of a set however need be used for the determination of distance and velocity.

In Fig. 10, the present system is illustrated as a whole with the exception of the interrupter oscillator 21 and the frequency modulator 28, which are omitted for the purpose of simplifying the drawing. In this figure, the spotting beam transmitter and receiver, shown as of the concentric type illustrated in Figs. 3 and 4, are shown connected to their respective circuits, whereas the circuits of the fan or searching beam are omitted for purposes of simplicity. However, the fan beam transmitter and receiver circuits are identicai with those of the concentric type.

In some possible applications of our invention it will be desired to use only a portion of the type of measurement it provides. For example, in spotting air targets in antiaircraft firing it will usually be sufiicient to locate the-target in azimuth and elevation and to measure the range. In its use as an altimeter for aircraft the distance measuring feature is all that is required. If velocity of climb is desired, the velocity can be measured by adding the frequency meter. For collision prevention a broad detecting beam and a distance indicator might be sufficient. Other arrangements will occur to those skilled in the art and will be deemed to be included in the scope of the appended claims.

We claim:

1. A system for the location of objects comprising means for projecting a fan-shaped beam, and a substantially cylindrically shaped beam of electromagnetic energy, means for swinging the projecting means for both said beams through corresponding angles, and means for swinging the projecting means for the cylindrical beam to cause the latter to move substantially in the plane of the fan-shaped beam.

2. The method of locating'aircraft or the like, which comprises projecting a radio beam of relatively small angular spread in one dimension and relatively large spread in the transverse direction, scanning a region of space with said beam, projecting a second beam having a uniform angular spread of the order of the spread of the first beam in its most limited direction, and moving said second beam along the plane of the first beam.

3. The method of locating aircraft or other object, which comprises projecting a fan-shaped high frequency radio beam, scanning a region of space with it, projecting a second substantially cylinder-shaped beam whose cross section is comparable with the thickening of the fan-shaped beam so that said second beam lies in the plane of the first beam, separately moving the second beam in the plane of the first beam, directionally receiving energy reflected from any point within the spread of the first beam, and separately directionally receiving energy reflected from any point within the spread of the second beam as the latter moves in the plane of the first beam and utilizing said received energy for directing said beams upon said .object.

4. The method of locating objects, which comprises generating and directing a radio beam of high frequency, detecting waves reflected by objects in said beam, alternately interrupting the beam and the detection of said reflected waves, and cyclically changing the frequency of interruption of the beam to render objects in any part of the beam detectable. v f

5. A system-for directing a beam of high frequency electromagnetic radiation and directional receiving means of said radiation toward an object reflecting said radiation, comprising a source of high frequency electromagnetic, beam radiation, an indicating instrument and two receivers of said radiation having directional characteristics. so arranged that they view overlapping but slightly difierent regions of space lying partially within said beam of radiation, said receivers having outputs arranged to be connected in opposition the two receivers having zones of reception so arranged with respect to the beam of radiation and their outputs being so combined as to produce opposite effects in said indicating instrument, whereby their combined effect is zero when a reflecting object is substantially in the center of the beam of radiation, and has a positive value when the reflecting object is on one side of the beam center, and a negative value when it is on the other side of the beam center.

6. Apparatus of the,characte r described having, in combination, radio transmitting means for I l projecting a fan-shaped beam of high frequency radio waves, means for turning the projecting means and hence the beam about an axis extending substantially parallel to the plane of the fanshaped beam, a receiver having a substantially columnar zone of reception, and means for turn-' ing said receiver and hence such zone of reception in the plane of said fan-shaped beam about an y, axis substantially at the apex of said fan-shaped beam.

7. Apparatus of the character described having, in combination, means for projecting a high frequency radio fan-shaped beam, meansgfor projecting a second high frequency radio beam substantially in the plane of the fan-shaped beam,

and means for swinging the second named means on an axis such that the second beam is moved along th fan-shaped beam.

8. Apparatus of the character described having, in combination, a focusing transmitting reflector, a transmitter disposed substantially at the focus of the reflector, the reflector being adapted to direct the radio energy of the transmitter upon a distant object from which the radio energy is adapted to be reflected, a focusing radio-receiving reflector disposed in the path of the radio energy after its reflection from the distant object. a pair of radio receivers disposed on opposite sides of the focus of the'focusing radio receiving reflector, a second pair of-receivers disposed on opposite sides of the focus of the focusing radio receiving reflector, the straight lines joining the receivers of one pair being substantially at right angles to the straight line joining the receivers of the other pair, and means for indicating the radio energy reflected by the focusing radio reflector upon the receivers.

9. Apparatus of the character described having, in combination, a focusing transmitter reflector,

a transmitter disposed substantially at the focus of the reflector, the' reflector being adapted to direct the radio energy of the transmitter upon a distant object from which the radio energy is adapted to be reflected back toward the reflector, a focusing radio-receiving reflector disposed behind the transmitter reflector in the path of return of the radio energy after its reflection from the distant object, the transmitter reflector being smaller than the receiving reflector to permit the transmitted radio energy, after its reflection from the distant object, to reach the receiving reflector,

and means for preventing interference between the transmitted and the received energy at the receiving reflector.

10. Apparatus of the character described having. in combination, a focusing transmitter reflector, a transmitter disposed substantially at the focus of the reflector, the reflector being adapted to direct the radio energy of the transmitter upon a distant object from which the radio energy is adapted to be reflected back toward the reflector,

a focusing radio-receiving reflector disposed behind the transmitter'reflector in the path of return of the radio energy after its reflection from the distant object, the transmitter reflector being smaller than the receivingreflector to permit the projected radio energy, after its reflection from the distant object, to reach the receiving reflector, a pair of receivers disposed on opposite sides of the-focus of the focusing radio receiving reflector, a second pair of receivers disposed on opposite sides of the focus of the focusing radio receiving reflector, the straight lines joining the receivers-oi one pair being substantially at right angles to the straight line joining the receivers of the other pair, and means for indicating the radio energy reflected by the focusing radio reflector upon the receivers.

11. Apparatus of the character described having, in combinationij'transmitter means for projecting a radio beam, means for varying the angular position of the beam in elevation and azimuth, a focusing reflector for receiving the beam afterreflection from a distant object, two pairs of radio receivers, the receivers of each pair being disposed respectively on opposite sides of the focus of the reflector, the pairs of receivers lying in planes extending at right angles to each other, and means for indicating the radio energy reflected by the reflector upon the receivers to indicate the elevational and azimuthal angles at which the beam is received by the reflector from the distant object.

12. Apparatus'of the character described having, in combination, transmitter means for projecting a beam, means for varying the direction of the beam,a focusing reflectorfor receiving the beam after reflection from a distant object, a pair of receivers disposed respectively at opposite sides of the focus of the reflector, and means responsive to the difference in the energy reflected by the reflector upon the respective receivers for indicating the direction at which the beam is received by the reflector from the distant object.

13. Apparatus of the character described having, in combination, means for projecting a radio beam, means for modulating the beam to produce pulses, means for receiving the pulses, means for alternately interrupting the operation of the projecting means and the receiving means to prevent interference between them, and means for varying the frequency of the modulating means to insure receipt of the pulses by the receiving means during periods of interruption of the operation of the projecting means.

14. In apparatus of the character described, a transmitter of high frequency radio waves for scanning a desired field of view, a pair of directional receivers arranged for receiving waves from said transmitter after reflection from an object in said field of view, said receivers being so disposed that their axes of maximum sensitivity are slightly offset with respect to each other, means for comparing the outputs of said receivers in opposition for indicating which of said axes passes nearest tothe object in the fleld of view,,and means for effecting simultaneous scanning of corresponding portions of said field of view by both said transmitter and receivers.

15, In apparatus of the character described, a transmitter of high frequency radio waves for scanning a desired field of view, a focussing receiving reflector, a pair of receiving antennae positioned on opposite sides of the focus of said reflector, means for moving said receiving reflector and said antennae to scan the field of view for receiving radiation from an object in said fleld of view reflecting the waves from said transmitter, radio receiver means connected for receiving the outputs of said antennae, said receiver means producing a reversible,.variable magnitude signal, an indicator, 9. control circuit for said indicator supplied with said variable magnitude signal, said indicator being operable from said signal for indicating the relative angular position of said reflector with respect to the object scanned.

16. In apparatus for locating remote objects, a high frequency transmitter having an emitting .17 antenna. reflecting means having a focus positioned substantially at said antenna for directionally controlling the emission therefrom, re-

ceiving means having antennae, and additional reflecting means having a focus disposed between said receiving antennae, one of said reflecting means being arranged behind the other and disposed substantially on a common axis therewith.

17. In apparatus for locating objects as defined in claim 16, wherein means is provided for moving said transmitter and receiver antennae and reflectors for directing the same upon the object, and indicating means operable from said receiver antennae for use in controlling said apparatus to direct the same at the object, thereby determining the position of the object.

18. The method of obtaining fire control data for antiaircraft guns, comprising sweeping the zenith with a fan shaped short wave radio beam, picking up any reflection of said beam by a radio receiver rotatable with said beam, thereby locating the target in one plane, and scanning the plane of the beam with a directional receiver until reflected waves are received thereby, whereby the bearings of the target are given in both planes.

19. The method of obtaining fire control data for antiaircraft guns, comprising sweeping the zenithwith a fan shaped short wave radio beam, picking up any reflection of said beam by a receiver rotatable with said beam, thereby locating the target in one plane, and scanning the plane of the beam with a directional substantially cylindrical beam and directional receiver until reflected waves are received thereby, whereby the bearings of the target are given in both planes.

20. In apparatus of the character described, means for projecting a fan-shaped beam of electromagnetic energy, means for receiving reflected electromagnetic energy having a zone of reception of fan shape that substantially coincides with said projected fan-shaped beam,'means for similarly orientating said beam and said zone of reception, and means for locating the position of reflecting objects along the spread or said fan-shaped beam,

W. HANSEN. RUSSELL H. VARIAN. I

Patent No. 2,415,094.

' WILLIAM W. HANSEN ET AL.

18 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,044,413 Weyrich June 16, 1936 1,965,632 Ewald July 10, 1934 2,085,798 Gerhard July 6, 1937 1,639,667 Ranger Aug. 23, 1927 1,945,952 Nicholson Feb. 6, 1934 2,033,937 Hollmann Mar. 17, 1936 2,085,022 Hollmann June 29, 1937 1,585,591 Lowy May 18, 1926 1,936,400 Langmuir Nov. 21, 1933 1,924,174 Wolf Aug. 29, 1933 2,106,771 Southworth Feb. 1, 1938 1,299,616 Rieber Apr. 8, 1919 1,372,043 Routin Mar. 22, 1921 1,400,990 Robin Dec. 20, 1921 1,962,582 Clavier June 12, 1934 1,999,884 Salzberg Apr. 30, 1935 2,038,992 Chaflee Apr. 28, 1936 2,101,440 Lindsell Dec. 7, 1937 2,073,643 Lindsell Mar, 16, 1937 2,116,717 Scharlau May 10. 1938 1,399,877 Pupin Dec. 13, 1921 1,904,534 Rice Apr. 18, 1933 894,318 De Forest July 28, 1908 1,872,975 Kolster Aug. 23, 1932 2,150,551 Kemp Mar. 14, 1939 1,838,371 Deardorfl Dec. 29, 1931 2,134,126 Hooven Oct. 25, 1938 FOREIGN PATENTS Number Country Date 384,325 British Dec. 5, 1932 422,659 British Jan. 16, 1935 440,238 British Dec. 23, 1935 426,328 British Apr. 2, 1935 429,863 British June 7, 1935 14,342 Norwegian Oct. 7, 1904 466,063 British May 21, 1937 455,765 British Oct. 27, 1936 OTHER REFERENCES "Wireless World (pages 623 and 624) June 26, 1938.

Certificate of Correction February 4, 1947.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 9, line 7, for side dimension read side of dimensions; line 8', after depth strike out of; line 9, for dimensions read dimension; column 12, line 41, for mixed read mixer; and that the said Letters Patent should be read with these corrections therein that the same may con form to the record of the case in the Patent Oflice.

Signed and sealed this 29th day Of'July, A. D. 1947.

LESLIE FRAZER,

First Assistant Gommissioner of Patents 

